Method of removing salamander from blast-furnace hearth



L. TOFFT Oct. 22, 1957 METHOD OF REMOVING SALAMANDER FROM BLAST-FURNACE HEARTH Filed Aug. 14, 1956 2 Sheets-Sheet 1 //VVE/VTOR.' LEONARD TOFFT,

his Ar/arney.

United States Patent METHOD OF REMOVING SALAMANDER FROM BLAST-FURNACE HEARTH Leonard Tofft, Orem, Utah, assignor to United States Steel Corporation, a corporation of New Jersey Application August 14, 1956, Serial No. 604,029

4 Claims. (Cl. 75-41) This invention relates generally to the operation of the iron blast-furnace and, more particularly, to the blowing-out of the furnace at the end of a campaign, and the removal, prior to blowing out, of the salamander or pool of molten iron which accumulates on the bottom block of the furnace in the cavity formed by erosion of the original hearth surface.

It has been the usual practice heretofore to tap the salamander by drilling a hole upwardly through the bottom block of the furnace. As an alternative, the salamander has been permitted to freeze after the furnace has been blown out, and then fragmented by blasting with explosives. These methods are troublesome and expensive. I have invented a novel method for bringing about the desired removal of a salamander, which is relatively simple and inexpensive yet highly effective.

In a preferred practice of my invention, I increase the angle of depression of the tap-hole with the horizontal in steps for several days prior to blowing out, and use excess clay in plugging the hole after each cast as needed, to maintain the tap-hole length substantially constant. Then, when the time for blowing out arrives, I alter the burden by charging an unusually heavy layer of coke and thereafter, alternate layers of coke and sinter or other filler material. I then continue to blow and charge the furnace, controlling the charging rate so that, when the heavy coke layer descends below the level of the tuyeres, the stock column has a height above the mantle substantially greater than normally existing on blowing out, thus maintaining the normal blast pressure and volume substantially undiminished. Then, after the heavy coke layer has descended below the level of the tuyeres, I make the final cast of molten iron from the furnace. On this cast, the greater portion by far of the salamander is forced out of the tapping hole by the blast pressure above the hearth.

A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawings illustrating the present preferred embodiment. In the drawings:

Figure l is a partial vertical section through the hearth of a blast-furnace, showing how the angle of depression of the tapping hole is increased and its length maintained; and

Figure 2 is a vertical section through the furnace up to the charging hopper, showing the condition of the burden at the time of the final cast, by which the salumander is almost wholly removed.

Referring now in detail to the drawings and, for the present, to Figure 1, a blast-furnace hearth of carbon blocks is confined within a steel shell 11. Formed in shell 11 is the usual iron notch 12 through which molten iron flows, on the opening of a tap hole normally closed by plugging with clay delivered into place by a conventional gun. Line 13 indicates the axis of the tap hole drilled for normal casts of iron from the furnace.

As the furnace campaign proceeds, the hearth 10 is ice eroded and, in the resulting cavity 14, a pool of molten iron 15, termed the salamander, accumulates. This accumulation results as the cavity erodes below the inner end of the tap hole, since no molten metal below that level can flow upwardly and out through the hole, on tapping, under the blast pressure in the furnace. When signs appear indicating the necessity for relining the furnace, the campaign is about at an end and preparations must be made for blowing out the furnace. According to my method, about a week below blowing out, I increase the angle of depression with the horizontal) of the tap holes drilled for the last few casts, in steps of about 5, from the original angle of about 25 to a final angle of about 40. Line 16 indicates the axis of the tap hole for the final cast.

In the normal operation of the furnace, i. e., before preparing for blowing out, I use excess clay in plugging the tap hole after successive casts so that, as a result, I build up a blister or thickened area 17 on the side of cavity 14 adjacent the inner end of the tap hole. I continue this practice during the final week. In this way, I ensure that the length of the tap hole will remain about the same, as the angle of depression thereof is increased. The end result, therefore, is that the inner end of the tap hole is lowered by a distance D into cavity 14. This will be about 2 or more in an average furnace of the size now customary.

After increasing the angle of depression of the tap hole in steps over about a week as explained above, the furnace is ready for blowing out. According to my invention, I make final preparation therefor by altering the composition of the burden in a particular way, as illustrated in Figure 2. Specifically, I discontinue charging slag-forming materials such as limestone and dolomite, and also medium-sized and larger ore. Instead of the normal charge, I introduce into the top of the furnace a layer of coke 18 from two to four times the thickness of the coke layer charged during normal operation. Next I charge alternate layers of iron-ore sinter and coke, of normal thickness, as indicated at 19 and 20, while continuing normal blast through the tuyeres 21, i. e., at substantially normal wind volume and blast pressure. Instead of sinter, I may charge ore, limestone, gravel or like filler material which will maintain the desired height of burden and still be easily removable by raking from the hearth.

With continued blowing, the burden descends after charging, in the normal manner, until coke layer 18 reaches the hearth 10. During this stage, I maintain the charging rate such that, when the coke layer 18 has descended below the level of the tuyeres, the height H of the stock column above the mantle 22 will be from one and a half to two times the usual height for blowing out. As an example, I maintain a stock-column height of from 40' to 50, preferably about 45', above the mantle, instead of the height of 20 to 30 as usually practiced. The increased height and the changed composition of the stock column permit the wind volume and blast pressure to be maintained substantially normal as aforementioned. Thas is to say, the increased height and decreased porosity of the column create a back pressure above the hearth which is substantially the same as that existing under normal operating conditions. In the absence of the procedure described, this pressure would be materially diminished from the normal value.

As a result of the steps described, on the final cast of molten metal through a tap hole drilled along axis 16, by far the greater portion of the salamander will be forced out through the hole by the internal pressure above the hearth. In a particular instance, I was able to remove all but a few hundred pounds of a salamander totaling about 300 tons. This small amount of iron remaining in cavity 14 is easily removed en masse when cooled. The remainder of the cavity is filled with a mixture of about 33% carbon, 60% slag-forming compounds (SiOz, A1303, CaO and MgO) and 4% iron, which can be readily broken up by hand tools. 'In other words, my method causes the slag normally floating on the molten iron, which is made up almost entirely of metal oxides, to be replaced by a semi-molten mass composed of about one-third carbon in solid lumps and two-thirds fused oxides. Thus the maintenance of substantially normal pressure above the hearth plus the lowering of the inner end of the tap hole, causes the salamander to be forced out in the final cast, except for a very small remainder, and this small imount of iron left after the final cast and the other material remaining on the hearth are in easily removable condition. After the final cast which clears out nearly all the molten iron from cavity 14, blowing out of the furnace is completed by following conventional procedure.

A few additional details of my practice should be observed. If, on making a normal cast, the tap hole is found shorter than usual, extra clay should be used on the next plugging to lengthen the hole by building up blister 17. The increased length of hole may require special precautions as to drying. For example, before a cast, the hole is drilled down to the moist region and allowed to vent for an hour or so. It is then drilled down to the iron skull in cavity 14 and dried for from 15 minutes to a half-hour with an oxygen lance before finally piercing the skull and tapping. The tap hole for the final cast is preferably made with a drill larger than that used for a normal cast, i. e., a 4" drill instead of the usual 3" drill.

Numerous advantages result from the method of my invention. In the first place, substantial economy in the time and cost of removing the salamander is achieved. The heavy coke layer which is first charged in preparation for blowing out, assures that the final cast will be above normal temperature and therefore quite fluid so the metal will readily flow to the tap hole when opened. The coke also produces a porous condition of the burden above the hearth which further contributes to this result. The inner end of the tap hole is lowered by as much as two feet or more before the final cast, thus assuring an almost complete removal of salamander iron.

Although I have disclosed herein the preferred practice and embodiment of my invention, I intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention.

Iclaim:

1. A method of removing the salamander from the hearth of an iron blast-furnace comprising progressively increasing the angle with the horizontal at which tap holes are drilled through the iron notch of the furnace for the last few casts of molten iron before the furnace is to be blown out; injecting excess clay through the tap holes beyond the amount needed for plugging after normal casts, sufficient to build up a blister on the hearth thereby maintaining the tap-hole length substantially constant as said angle is increased; then, when said angle is about charging an extra-heavy layer of coke into the furnace and thereafter charging alternate layers of coke and other burden material; continuing the blowing and charging of the furnace thereby maintaining a stock column of a height and character such that normal wind volume and pressure of the furnace blast remain substantially undiminished; and when the extra-heavy coke layer has descended to the level of the furnace tuyeres, making a final cast of molten iron from the hearth whereby the far greater portion of the salamander is forced out leaving on the hearth only a small portion thereof and a frangible mixture of iron with carbon and slag.

2. A method as defined by claim 1, characterized by increasing said angle in steps of about 5".

3. A method as defined by claim 1, characterized by maintaining said stock-column height from 40 to feet.

4. A method as defined by claim 1, characterized by said mixture comprising about 33% carbon, slag and 4% iron.

No references cited. 

1. A METHOD OF REMOVING THE SALAMANDER FROM THE HEARTH OF AN IRON BLAST-FURNACE COMPRISING PROGESSEIVELY INCREASING THE ANGLE WITH THE HORIZONTAL AT WHICH TAP HOLES ARE DRILLED THROUGH THE IRON NOTCH OF THE FURNACE FOR THE LAST FEW CASTS OF MOLTEN IRON BEFORE THE FURNACE IS TO BE BLOWN OUT; INJECTING EXCESS CLAY THROUGH THE TAP HOLES BEYOND THE AMOUNT NEEDED FOR PLUGGING AFTER NORMAL CASTS, SUFFICIENT TO BUILD UP A BLISTER ON THE HEARTH THEREBY MAINTAINING THE TAP-HOLE LENGTH SUBSTANTIALLY CONSTANT AS SAID ANGLE IS INCREASED; THEN, WHEN SAID ANGLE IS ABOUT 40*, CHARGING AN EXTRA-HEAVY LAYER IF COKE INTO THE FURNACE AND THEREAFTER CHARGING ALTERNATE LAYERS OF COKE AND OTHER BURDEN MATERIAL; CONTINUING THE BLOWING AND CHARGING OF THE FURNACE THEREBY MAINTAINING A STOCK COLUMN OF A HEIGHT AND CHARACTER SUCH THAT NORMAL WIND VOLUME AND PRESSURE OF THE FURNACE THEREBY BLAST REMAIN SUBSTANTIALLY UNDIMINISHED; AND WHEN THE EXTRA-HEAVY COKE LAYER HAS DESCENDED TO THE LEVEL OF THE FURNACE TUYERES, MAKING A FINAL CAST OF MOLTEN IRON FROM THE HEARTH WHEREBY THE FAR GREATER PORTION OF THE SALAMANDER IS FORCED OUT LEAVING ON THE HEARTH ONLY A SMALL PORTION THEREOF AND A FRANGIBLE MIXTURE OF IRON WITH CARBON AND SLAG. 